A coextrusion feedblock is used to bring together molten streams of thermoplastic materials from multiple extruders. Individual streams from different extruders are brought together in the coextrusion feedblock to form a particular layer structure. The resulting multi-layer extrudate flow is then delivered to a subsequent extrusion die to produce the desired multiple layer extrudate.
In the case of a coextrusion feedblock adapted for producing 3-layer structures, the feedblock may initially be set-up for producing an A/B/C layer structure. If the operator later wishes to produce an A/C/B layer structure, for example, then with conventional feedblocks, it is first necessary to shut down the line and replace components, such as flow inserts, diverters, plugs, flow spools, and/or selector plates. Significant downtime results from replacing such parts and restringing the line for the new layer structure. This downtime can be on the order of hours.
Recent developments have focused on allowing extrusion die operators to adjust feed blocks from one configuration to another configuration to produce different layered structures, without having to shut down the extruder and/or dissemble the device. U.S. Pat. No. 8,490,643 to Hanson et al. (Hanson) teaches a diverter valve used for a coextrusion feed block that has a body and an axially moveable valve piston in the body. Axial movement of the valve piston from a first position to a second position transitions the flow paths from first flow configuration that produces one type of multi-layered extrudate to a second flow configuration that produces another type of multi-layered structure. Hanson's diverter valve allows the operator to transition between the two-extrudate configurations without having to shut down the extrusion die. The present inventor developed a diverter valve with a monolithic rotating spool. Instead of axially moving a valve piston to alter flow configurations as in Hanson, the spool rotates between two configurations to alter the flow paths and produce different layered structures. U.S. Patent App. Pub. No. 2016/0243743 to Hanson et al. (Hanson II) teaches a two-part rotating cylindrical spool. The two-part spool has a first half with a recess and a second half with another recess. The two-part spool is rotated in sequence, which helps prevent polymer dead head in the diverter valve as the diverter valve transitions between different flow configurations.